Method of manufacturing a semiconductor device having a group-iii nitride superlattice layer on a silicon substrate

ABSTRACT

Provided is a semiconductor device containing a silicon single crystal substrate  101 , a silicon carbide layer  102  provided on a surface of the substrate, a Group III nitride semiconductor junction layer  103  provided in contact with the silicon carbide layer, and a superlattice-structured layer  104  constituted by Group III nitride semiconductors on the Group III nitride semiconductor junction layer. In this semiconductor device, the silicon carbide layer is a layer of a cubic system whose lattice constant exceeds 0.436 nm and is not more than 0.460 nm and which has a nonstoichiometric composition containing silicon abundantly in terms of composition, and the Group III nitride semiconductor junction layer has a composition of Al x Ga Y In z N 1-α M α  ( 0 ≦X, Y, Z≦1, X+Y+Z=1, 0≦α&lt;1, M is a Group V element except nitrogen).

CROSS-REFERENCE RELATED APPLICATIONS

This application is a Rule 53(b) Divisional of U.S. patent applicationSer. No. 12/063,002 filed Mar. 10, 2008, which is a 371 of PCTApplication No. PCT/JP2006/315978 filed Aug. 7, 2006, which claimsbenefit to Japanese Patent Application No. 2005-229426 filed Aug. 8,2005. The above-noted applications are incorporated herein by referencein their entirety.

TECHNICAL FIELD OF

The present invention relates to a semiconductor device formed from astacked structure having a substrate of a silicon single crystal and aGroup III nitride semiconductor layer.

BACKGROUND ART

Gallium nitride (GaN) and aluminum nitride (AlN) have (hitherto) beenknown as Group III nitride semiconductors. These Group III nitridesemiconductor materials are used to form semiconductor light emittingdevices, such as light emitting diodes (hereinafter abbreviated as“LEDs”), which emit blue, green or otherwise visible light of shortwavelength, and laser diodes (hereinafter abbreviated as “LDs”) (referto, for example, JP-A SHO 55-3834 (Patent Document 1)). Also, theseGroup III nitride semiconductor materials are used to form electronicdevices such as high-frequency transistors (refer to, for example, M. A.Kahn et al., Applied Physics Letters (Appl. Phys. Lett.), USA, 1993,Vol. 62, p. 1786 (Non-patent Document 1)).

In such semiconductor devices composed of Group III nitridesemiconductor materials, a sapphire (α-Al₂O₃) bulk single crystal (referto, for example, JP-A HEI 6-151943 (Patent Document 2) or a cubicsilicon carbide (SiC) bulk single crystal (refer to, for example, JP-AHEI 6-326416 (Patent Document 3)) is used as a substrate. LEDs have beenmanufactured by using, for example, a stacked structure having acladding layer composed of a Group III nitride semiconductor material,and a light emitting layer and the like on a sapphire substrate (referto, for example, JP-A HWI 6-151966 (Patent Document 4)).

However, because sapphire, which is used as a material for the substrateof a Group III nitride semiconductor device, has electrical insulatingproperties, the material has for example the problem that it is not easyto obtain Group III nitride LEDs having high breakdown voltageproperties against static electricity and the like. However, becausesapphire does not have high thermal conductivity, it has been difficultto fabricate field-effect transistors (hereinafter abbreviated as“FETs”) of low loss in which the heat radiating properties of asubstrate are utilized. If a silicon carbide bulk single crystal thathas electrical conductivity and excellent thermal conductivity is usedas a substrate, this is convenient for forming FETS having excellentbreakdown voltage properties against static electricity and the like andFETs having excellent heat radiating properties. However, a siliconcarbide bulk single crystal having a diameter that is appropriatelylarge for use in a substrate is expensive and this is unfavorable forthe manufacture of consumer Group III nitride semiconductor devices.

On the other hand, a silicon single crystal (hereinafter sometimesreferred to as “silicon”) inherently has high thermal conductivity andbesides large-diameter single crystals having high electric conductivityhave already been mass produced. Therefore, if silicon having highconductivity and a large diameter is used as a substrate, it is expectedthat, for example, inexpensive consumer LEDs having high breakdownvoltage properties against static electricity and the like can be putinto practical use. Furthermore, if silicon that has a high thermalconductivity in spite of high resistance is used in a substrate, it isexpected that low-loss FETs for high-frequency band communication can berealized. However, the lattice constant (=a) of a silicon single crystalis 0.543 nm and the a-axis lattice constant of a Group III nitridesemiconductor, for example, of hexagonal GaN is 0.319 nm. Therefore, alarge lattice mismatch exists between the two materials. The mismatch isalso large between cubic GaN (a=0.451 nm) and a silicon single crystal.For this reason, a silicon single crystal has the disadvantage that itis difficult to stably form a superior-quality Group III nitridesemiconductor layer having few crystal defects on a silicon singlecrystal substrate.

It is according to conventional arts that in providing a Group IIInitride semiconductor layer on a single crystal substrate having a largelattice mismatch, a buffer layer for reducing the lattice mismatchbetween the two is provided. In conventional arts, a buffer layer isformed from Group III nitride semiconductor materials of, for example,AlN and GaN (refer to, for example, JP-A HEI 6-314659 (Patent Document5)). However, the mismatch between a silicon single crystal and cubic orhexagonal AlN or GaN is large, and lattice strains cannot besufficiently relieved. For this reason, if a Group III nitridesemiconductor layer is formed by using a buffer layer composed of aconventional Group III nitride semiconductor material, it is impossibleto stably form a Group III nitride semiconductor layer excellent incrystallinity, thereby posing a problem.

Also, there has been known a conventional art that involves, in theformation of a Group III nitride semiconductor layer on a silicon singlecrystal as a substrate, forming a Group III nitride semiconductor layervia a thin film layer of cubic 3C-type silicon carbide (3C—SiC) (referto, for example, T. Kikuchi et al., Journal of Crystal Growth (J.Crystal Growth), the Netherlands, 2005, Vol. 171, No. 1-2, page e1215 topage e1221 (Non-patent Document 2)). However, this technique has thedisadvantage that depending on the properties of a 3C—SiC thin filmlayer, the crystallinity and the like of a Group III nitridesemiconductor layer, which is an upper layer of the 3C—SiC thin filmlayer, change remarkably, with the result that it is impossible tostably form a superior Group III nitride semiconductor layer. Also, thistechnique poses the problem that even when a buffer layer composed ofSiC is used, a Group III nitride semiconductor layer formed thereoncannot always be excellent in surface flatness.

Single crystals excellent in electrical conductivity and heat radiatingproperties have already been mass produced. In order to obtain asemiconductor device that is excellent in optical and electricalproperties and uses a silicon single crystal as a substrate, it isnecessary to use a buffer layer that is configured to advantageouslyreduce a lattice mismatch with a substrate and to be able to lead to theformation of a good-quality Group III nitride semiconductor layer. Forexample, even when an SiC layer is used as a buffer layer in forming aGroup III nitride semiconductor layer on a silicon single crystalsubstrate, it is necessary to use an SiC buffer layer that is configuredto be able to advantageously reduce a lattice mismatch between the twomaterials.

Furthermore, in addition to the use of an SiC buffer layer that isconfigured to be effective in reducing a lattice mismatch, it isnecessary to produce an original idea in a stacked structure above thebuffer layer that leads to the formation of a good-quality Group IIInitride semiconductor layer excellent in surface flatness as well as incrystallinity. Also, in order to manufacture a semiconductor devicehaving excellent properties, it is necessary to use a manufacturingmethod for leading to stably forming the SiC buffer layer and thegood-quality Group III nitride semiconductor layer excellent in surfaceflatness.

The object of the present invention is to provide a semiconductor devicehaving a buffer layer capable of advantageously reducing a latticemismatch with a substrate.

Another object of the present invention is to provide a high-performancesemiconductor device that leads to the formation of a good-quality GroupIII nitride semiconductor layer excellent in crystallinity and surfaceflatness.

Still another object of the present invention is to provide a method ofmanufacturing a semiconductor device capable of stably fabricating anSiC buffer layer that effectively reduces a lattice mismatch and asuperior-quality Group III nitride semiconductor layer excellent insurface flatness.

DISCLOSURE OF THE INVENTION

To achieve the above-described objects, in a semiconductor devicecomprising a silicon single crystal substrate, a silicon carbide (SIC)layer provided on a surface of the substrate, a Group III nitridesemiconductor junction layer provided in contact with the siliconcarbide layer, and a superlattice-structured layer constituted by GroupIII nitride semiconductors on the Group III nitride semiconductorjunction layer, the semiconductor device of the present invention ischaracterized by (1) using a silicon single crystal as a substrate andcomprising a silicon carbide layer, which is provided on the substrateand composed of cubic silicon carbide whose lattice constant exceeds0.436 nm and is not more than 0.460 nm, and which has anonstoichiometric composition containing silicon abundantly in terms ofcomposition, a Group III nitride semiconductor junction layer having acomposition of Al_(x)Ga_(y)In_(z)N_(1-α)M_(α) (0≦X, Y, Z≦1, X+Y+Z=1, thesymbol M denotes a Group V element except nitrogen and 0≦α<1), which isprovided on the silicon carbide layer, and a superlattice-structuredlayer constituted by Group III nitride semiconductors, which is providedon the Group III nitride semiconductor junction layer.

Particularly, the semiconductor device related to the present inventionis characterized in that (2) in the semiconductor device described initem (1) above, the superlattice-structured layer provided on the GroupIII nitride semiconductor junction layer is formed by alternatelystacking aluminum-gallium nitride (composition formula: Al_(x)Ga_(1-x)N:0≦X≦1) layers having different aluminum (Al) composition ratios.

Particularly, the semiconductor device related to the present inventionis characterized in that (3) in the semiconductor device described initem (2) above, a layer having a lower Al composition ratio (═X) amongthe aluminum gallium nitride (Al_(x)Ga_(1-x)N: 0≦X≦1) layersconstituting the superlattice-structured layer is provided so as to bebonded to the Group III nitride semiconductor junction layer.

Particularly, the semiconductor device related to the present inventionis characterized in that (4) in the semiconductor device described initem (1) above, the superlattice-structured layer is formed byalternately stacking gallium-indium nitride (composition formula:Ga_(Q)In_(1-Q)N: 0≦Q≦1) layers having different gallium (Ga) compositionratios.

Particularly, the semiconductor device related to the present inventionis characterized in that (5) in the semiconductor device described initem (4) above, a layer having a larger gallium composition ratio (=Q)among the gallium-indium nitride (Ga_(Q)In_(1-Q)N: 0≦Q≦1) layersconstituting the superlattice-structured layer is provided so as to bebonded to the Group III nitride semiconductor junction layer.

Particularly, the semiconductor device related to the present inventionis characterized in that (6) in the semiconductor device described inany one of items (1) to (5) above, the Group III nitride semiconductorsuperlattice-structured layer is constituted by Group III nitridesemiconductor layers having a film thickness from monolayers (MLs) to 30MLs.

Particularly, the semiconductor device related to the present inventionis characterized in that (7) in the semiconductor device described inany one of items (1) to (6) above, the substrate is a (111) siliconsingle crystal whose surface is a (111) crystal plane, and in that theGroup III nitride semiconductor junction layer is composed of hexagonalwurtzite crystal type aluminum nitride (AlN).

Particularly, the semiconductor device related to the present inventionis characterized in that (8) in the semiconductor device described inany one of items (1) to (6) above, the substrate is a (001) siliconsingle crystal whose surface is a (001) crystal plane, and in that theGroup III nitride semiconductor junction layer is composed of cubic zincblende crystal type aluminum nitride (ALM).

Also, in a method of manufacturing a semiconductor device comprising asubstrate composed of a silicon single crystal, a silicon carbide layerprovided on a surface of the silicon single crystal substrate, a GroupIII nitride semiconductor junction layer provided so as to be bonded tothe silicon carbide layer, and a superlattice-structured layerconstituted by Group III semiconductors, which is provided on the GroupIII nitride semiconductor junction layer, the method of manufacturing asemiconductor device of the present invention is characterized by (A)including the steps of: (1) blowing a hydrocarbon gas onto a surface ofa silicon single crystal substrate and thereby causing hydrocarbon to beadsorbed onto a crystal plane that is the surface of the substrate; (2)thereafter heating the silicon single crystal substrate to a temperatureof not less than a temperature at which the hydrocarbon is adsorbed,thereby forming, on the surface of the silicon single crystal substrate,a cubic silicon carbide layer whose lattice constant exceeds 0.436 nmand is not more than 0.460 nm and which has a nonstoichiometriccomposition containing silicon abundantly in terms of composition; (3)thereafter supplying a gas containing a Group V element and a gascontaining Group III element to the surface of the silicon carbide layerand thereby forming a Group III nitride semiconductor junction layer;and (4) thereafter forming a superlattice-structured layer constitutedby Group III nitride semiconductors on the Group III nitridesemiconductor junction layer.

Particularly, the method of manufacturing a semiconductor device of thepresent invention is characterized by (B) involving, in themanufacturing method described in item (A) above, using a (111) siliconsingle crystal whose surface is a (111) crystal plane as the substrate,forming, on the surface of the substrate, a cubic silicon carbide layerwhich has a nonstoichiometric composition containing silicon abundantlyin terms of composition and whose surface is a (111) crystal planesilicon carbide layer, thereafter forming a hexagonal Group III nitridesemiconductor junction layer on the surface of the silicon carbidelayer, and thereafter forming a superlattice-structured layerconstituted by hexagonal Group III nitride semiconductors on the surfaceof the Group III nitride semiconductor junction layer.

Particularly, the method of manufacturing a semiconductor device of thepresent invention is characterized by (C) involving, in themanufacturing method described in item (A) above, using a (001) siliconsingle crystal whose surface is a (001) crystal plane as the substrate,forming, on the surface of the substrate, a cubic silicon carbide layerwhich has a nonstoichiometric composition containing silicon abundantlyin terms of composition and whose surface is a (001) crystal planesilicon carbide layer, thereafter forming a cubic Group III nitridesemiconductor junction layer on the surface of the silicon carbidelayer, and thereafter forming a superlattice-structured layerconstituted by cubic Group III nitride semiconductors on the surface ofthe Group III nitride semiconductor junction layer.

Particularly, the method of manufacturing a semiconductor device of thepresent invention is characterized by (D) involving, in themanufacturing method described in item (B) or (C) above, forming asilicon carbide layer which has a nonstoichiometric compositioncontaining silicon abundantly in terms of composition on the surface ofthe substrate formed from a silicon single crystal, and thereafterforming a Group III nitride semiconductor junction layer composed ofaluminum nitride by supplying a gaseous raw material containing aluminumand a gaseous raw material containing nitrogen to the surface of thesilicon carbide.

Particularly, the method of manufacturing a semiconductor device of thepresent invention is characterized by (E) involving, in themanufacturing method described in item (D) above, forming a siliconcarbide layer which has a nonstoichiometric composition containingsilicon abundantly in terms of composition on the surface of thesubstrate composed of a silicon single crystal, thereafter causing analuminum film to be deposited on the surface of the silicon carbidelayer by supplying a gaseous raw material containing aluminum,thereafter nitriding the aluminum film by supplying a gaseous rawmaterial containing nitrogen, and forming an aluminum nitride layer.

Particularly, the method of manufacturing a semiconductor device of thepresent invention is characterized by (F) involving, in themanufacturing method described in item (D) above, blowing a hydrocarbongas to the surface of the substrate composed of a silicon single crystaland causing the hydrocarbon to be adsorbed onto the surface of thesilicon single crystal substrate while radiating electrons.

Particularly, the method of manufacturing a semiconductor device of thepresent invention is characterized by (G) involving, in themanufacturing method described in item (F) above, after causinghydrocarbon to be adsorbed onto the surface of the substrate composed ofa silicon single crystal, heating the silicon single crystal substratewhile radiating electrons to a temperature of not less than atemperature at which the hydrocarbon is caused to be adsorbed, therebyforming, on the surface of the silicon single crystal substrate, a cubicsilicon carbide layer whose lattice constant exceeds 0.436 nm and is notmore than 0.460 nm and which has a nonstoichiometric compositioncontaining silicon abundantly in terms of composition.

That is, the present invention relates to the following:

[1] A semiconductor device comprising a silicon single crystalsubstrate, a silicon carbide layer provided on a surface of thesubstrate, a Group III nitride semiconductor junction layer provided incontact with the silicon carbide layer, and a superlattice-structuredlayer constituted by Group III nitride semiconductors on the Group IIInitride semiconductor junction layer, which is characterized in that thesilicon carbide layer is a layer of a cubic system whose latticeconstant exceeds 0.436 nm and is not more than 0.460 nm and which has anonstoichiometric composition containing silicon abundantly in terms ofcomposition, and in that the Group III nitride semiconductor junctionlayer has a composition of Al_(x)Ga_(Y)In_(z)N_(1-α)M_(α) (0≦X, Y, Z≦1,X+Y+Z=1, 0≦α<1, M is a Group V element except nitrogen).[2] The semiconductor device described in item [1] above, which ischaracterized in that the superlattice-structured layer constituted byGroup III nitride semiconductors is a layer formed by alternatelystacking aluminum-gallium nitride (Al_(x)Ga_(1-x)N: 0≦X≦1) layers havingdifferent aluminum (Al) composition ratios.[3] The semiconductor device described in item [2] above, which ischaracterized in that a layer having a low Al composition ratio amongthe aluminum-gallium nitride layers having different aluminumcomposition ratios is in contact with the Group III nitridesemiconductor junction layer.[4] The semiconductor device described in item [1] above, which ischaracterized in that the superlattice-structured layer constituted byGroup III nitride semiconductors is a layer formed by alternatelystacking gallium-indium nitride (Ga_(Q)In_(1-Q)N: 0≦Q≦1) layers havingdifferent gallium (Ga) composition ratios.[5] The semiconductor device described in item [4] above, which ischaracterized in that a layer having a high gallium (Ga) compositionratio among the gallium-indium nitride layers having different gallium(Ga) composition ratios is in contact with the Group III nitridesemiconductor junction layer.[6] The semiconductor device described in any one of items [1] to [5]above, which is characterized in that the superlattice-structured layerconstituted by Group III nitride semiconductors has a film thickness of5 monolayers (MLs) to 30 MLs.[7] The semiconductor device described in any one of items [1] to [6]above, which is characterized in that the silicon single crystalsubstrate is a substrate whose surface is a (111) crystal plane, and inthat the Group III nitride semiconductor junction layer is a hexagonalwurtzite crystal type aluminum nitride (AlN) layer.[8] The semiconductor device described in any one of items [1] to [6]above, which is characterized in that the silicon single crystalsubstrate is a substrate whose surface is a (001) crystal plane, and inthat the Group III nitride semiconductor junction layer is a cubic zincblende crystal type aluminum nitride (AlN) layer.[9] A method of manufacturing a semiconductor device that ischaracterized by including in this order: (1) the step of blowing ahydrocarbon gas onto a surface of a silicon single crystal substrate andcausing the hydrocarbon to be adsorbed onto the surface of thesubstrate; (2) the step of heating the silicon single crystal substrateto a temperature of not less than a temperature at which the hydrocarbonis caused to be adsorbed, thereby forming, on the surface of the siliconsingle crystal substrate, a cubic silicon carbide layer whose latticeconstant exceeds 0.436 nm and is not more than 0.460 nm and which has anonstoichiometric composition containing silicon abundantly in terms ofcomposition; (3) the step of supplying a gas containing a Group Velement and a gas containing Group III element to the surface of thesilicon carbide layer, thereby forming a Group III nitride semiconductorjunction layer; and (4) the step of forming a superlattice-structuredlayer constituted by Group III nitride semiconductors on the Group IIInitride semiconductor junction layer.[10] The method of manufacturing a semiconductor device described initem [9] above, which is characterized in that the silicon singlecrystal substrate is a substrate whose surface is a (111) crystal plane,in that the silicon carbide layer formed on the substrate surface is alayer whose surface is a (111) crystal plane, in that the Group IIInitride semiconductor junction layer is a hexagonal layer, and in thatthe superlattice-structured layer constituted by Group III nitridesemiconductors is a hexagonal layer.[11] The method of manufacturing a semiconductor device described initem [9] above, which is characterized in that the silicon singlecrystal substrate is a substrate whose surface is a (001) crystal plane,in that the silicon carbide layer formed on the substrate surface is alayer whose surface is a (001) crystal plane, in that the Group IIInitride semiconductor junction layer is a cubic layer, and in that thesuperlattice-structured layer constituted by Group III nitridesemiconductors is a cubic layer.[12] The method of manufacturing a semiconductor device described in anyone of items [9] to [11] above, which is characterized in that in thestep (3), a Group III nitride semiconductor junction layer is formed bysupplying a raw material containing aluminum as a gas containing a GroupIII element and a raw material containing nitrogen as a gas containing aGroup V element.[13] The method of manufacturing a semiconductor device described in anyone of items [9] to [12] above, which is characterized in that the step(3) comprises: (3a) forming a layer containing a Group III element bysupplying a gas containing a Group III element to the surface of thesilicon carbide layer; and (3b) forming a nitride layer of a Group IIIelement as the Group III nitride semiconductor junction layer bynitriding a layer containing a Group III element.[14] The method of manufacturing a semiconductor device described initem [13] above, which is characterized in that in the step (3a), analuminum layer is formed by supplying a gas containing aluminum to thesurface of the silicon carbide surface as a gas containing a Group IIIelement.[15] The method of manufacturing a semiconductor device described in anyone of items [9] to [14] above, which is characterized in that the step(1) comprises the step (1a) that involves blowing a hydrocarbon gas ontothe surface of the silicon single crystal substrate and causing thehydrocarbon to be adsorbed onto the surface of the substrate byradiating electrons.[16] The method of manufacturing a semiconductor device described in anyone of items [9] to [14] above, which is characterized in that the steps(1) and (2) comprise the step (1b) that involves, after causinghydrocarbon to be adsorbed onto the surface of the silicon singlecrystal substrate, heating the silicon single crystal substrate whileradiating electrons to a temperature of not less than a temperature atwhich the hydrocarbon is caused to be adsorbed, thereby forming, on thesurface of the silicon single crystal substrate, a cubic silicon carbidelayer whose lattice constant exceeds 0.436 nm and is not more than 0.460nm and which has a nonstoichiometric composition containing siliconabundantly in terms of composition.

According to the present invention, in a semiconductor device comprisinga substrate composed of a silicon single crystal, a silicon carbidelayer provided on a surface of the substrate, a Group III nitridesemiconductor junction layer provided so as to be bonded to the siliconcarbide layer, and a superlattice-structured layer constituted by GroupIII nitride semiconductors on the Group III nitride semiconductorjunction layer, the semiconductor device of the present invention issuch that a silicon single crystal is used as the substrate, a bufferlayer is composed of cubic silicon carbide, which is provided on thesubstrate, whose lattice constant exceeds 0.436 nm and is not more than0.460 nm and which has a nonstoichiometric composition containingsilicon abundantly in terms of composition, a Group III nitridesemiconductor junction layer having a composition ofAl_(x)Ga_(y)In_(z)N_(1-α)M_(α) (0≦X, Y, Z≦1, X+Y+Z=1, the symbol Mdenotes a Group V element except nitrogen (N) and 0≦α<1), is provided onthe silicon carbide layer, and a superlattice-structured layerconstituted by Group III nitride semiconductors is further provided onthe Group III nitride semiconductor junction layer, whereby a stackedstructure is formed. And the semiconductor device is obtained by usingthe stacked structure. Accordingly, it is possible to form agood-quality Group III nitride semiconductor layer excellent incrystallinity and surface flatness and, therefore, it is possible toprovide a high-performance semiconductor device.

Particularly, in the present invention, the superlattice-structuredlayer provided on the Group III nitride semiconductor junction layer isformed by alternately stacking Al_(x)Ga_(1-x)N (0≦X≦1) layers havingdifferent aluminum composition ratios. Accordingly, it is possible tostably form a good-quality Group III nitride semiconductor layerexcellent in crystallinity and surface flatness and, therefore, this iseffective in stably providing a high-performance semiconductor device.

Particularly, also in the present invention, in providing thesuperlattice-structured layer constituted by Al_(x)Ga_(1-x)N (0≦X≦1)layers having different aluminum contents, the stacked structure is suchthat a layer having a lower Al composition ratio (═X) among theAl_(x)Ga_(1-x)N (0≦X≦1) layers constituting the superlattice structureis provided so as to be bonded to the Group III nitride semiconductorjunction layer. Therefore, particularly, it is possible to form a GroupIII nitride semiconductor layer excellent in surface flatness and thiscan contribute to obtaining a high-performance semiconductor device.

Particularly, also in the present invention, the superlattice-structuredlayer provided on the Group III nitride semiconductor junction layer isformed by alternately stacking (Ga_(Q)In_(1-Q)N: (0≦Q≦1)) layers havingdifferent gallium (Ga) composition ratios. Accordingly, it is possibleto stably form a good-quality Group III nitride semiconductor layerexcellent in crystallinity and surface flatness and, therefore, this iseffective in stably providing a high-performance semiconductor device.

Particularly, also in the present invention, in providing thesuperlattice-structured layer constituted by Ga_(Q)In_(1-Q)N (0≦Q≦1)layers, a gallium-indium nitride layer having a higher gallium (Ga)composition ratio (=Q) among the Ga_(Q)In_(1-Q)N (0≦Q≦1) layersconstituting the superlattice-structured layer is provided so as to bebonded to the Group III nitride semiconductor junction layer. Therefore,particularly, it is possible to form a Group III nitride semiconductorlayer excellent in surface flatness and this can contribute to obtaininga high-performance semiconductor device.

Particularly, in the present invention, the superlattice-structuredlayer is constituted by Al_(x)Ga_(1-x)N (0≦X≦1) layers orGa_(Q)In_(1-Q)N (0≦Q≦1) layers having film thicknesses of 5 MLs to 30MLs. Therefore, particularly, it is possible to form a Group III nitridesemiconductor layer excellent in surface flatness and this cancontribute to stably obtaining a high-performance semiconductor device.

Particularly, in the present invention, a (111) silicon single crystalis used as the substrate and the Group III nitride semiconductorjunction layer provided on the surface of the semiconductor via an SiCbuffer layer is formed from a wurtzite crystal typeAl_(x)Ga_(Y)In_(z)N_(1-α)M_(α) (0≦X, Y, Z≦1, X+Y+Z=1, the symbol Mdenotes a Group V element except nitrogen (N) and 0≦α<1). Therefore, thesuperlattice-structured layer and the like provided on the Group IIInitride semiconductor junction layer can be formed in a unified mannerfrom the hexagonal Group III nitride semiconductor layer. Accordingly,this is advantageous for obtaining a semiconductor device capable ofexhibiting the properties based on hexagonal Group III nitridesemiconductor materials.

Particularly, in the present invention, a (001) silicon single crystalwhose surface is a (001) crystal plane is used as the substrate, and theGroup III nitride semiconductor junction layer provided on the surfaceof the substrate via an SiC buffer layer is formed from a cubiczincblende crystal type Al_(x)Ga_(Y)In_(z)N_(1-α)M_(α) (0≦X, Y, Z≦1,X+Y+Z=1, the symbol M denotes a Group V element except nitrogen (N), and0≦α<1). Therefore, the superlattice-structured layer and the likeprovided on the Group III nitride semiconductor junction layer can beformed in a unified manner from the cubic Group III nitridesemiconductor layer. Accordingly, this is advantageous for obtaining asemiconductor device capable of exhibiting the properties based on cubicGroup III nitride semiconductor materials.

Also, in the present invention, in manufacturing a semiconductor devicecomprising a substrate composed of a silicon single crystal, a siliconcarbide layer provided on a surface of the silicon single crystalsubstrate, a Group III nitride semiconductor junction layer provided soas to be bonded to the silicon carbide layer, and asuperlattice-structured layer constituted by Group III semiconductors,which is provided on the Group III nitride semiconductor junction layer,a hydrocarbon gas is blown onto a surface of a silicon single crystalsubstrate and the hydrocarbon is caused to be adsorbed onto a crystalplane that is the surface of the substrate. And thereafter the siliconsingle crystal substrate is heated to a temperature of not less than atemperature at which the hydrocarbon is caused to be adsorbed, wherebythe silicon carbide layer is formed. Therefore, it is possible topositively form, on the surface of the silicon single crystal substrate,a cubic silicon carbide layer whose lattice constant exceeds 0.436 nmand is not more than 0.460 nm and which has a nonstoichiometriccomposition containing silicon abundantly in terms of composition. Andhence it is possible to obtain a Group III nitride semiconductorjunction layer composed of good-quality Al_(x)Ga_(y)In_(z)N_(1-α)M_(α)(0≦X, Y, Z≦1, X+Y+Z=1, the symbol M represents a Group V element exceptnitrogen (N) and 0≦α<1), which is provided on the silicon carbide layer,and a superlattice-structured layer constituted by Group III nitridesemiconductors, which is further provided on the Group III nitridesemiconductor junction layer. Therefore, it is possible to manufacture asemiconductor device having excellent properties, which reflect theexcellent crystallinity of these semiconductor layers.

Particularly, according to the present invention, a (111) silicon singlecrystal whose surface is a (111) crystal plane is used as the substrate,a cubic (111) silicon carbide layer which has a nonstoichiometriccomposition containing silicon abundantly in terms of composition andwhose surface is a (111) crystal plane is formed on the surface of thesubstrate, a Group III nitride semiconductor junction layer composed ofhexagonal Al_(x)Ga_(y)In_(z)N_(1-α)M_(α) (0≦X, Y, Z≦1, X+Y+Z=1, thesymbol M denotes a Group V element except nitrogen and 0≦α<1) is formedon the surface of the silicon carbide layer, thereafter asuperlattice-structured layer constituted by hexagonal Group III nitridesemiconductors is formed, whereby a semiconductor device is formedthrough these steps. Therefore, it is possible to manufacture asemiconductor device capable of advantageously exhibiting optical orelectrical properties based on the crystal properties of the hexagonalGroup III nitride semiconductor.

Particularly, according to the present invention, a (001) silicon singlecrystal whose surface is a (001) crystal plane is used as the substrate,a cubic silicon carbide layer which has a nonstoichiometric compositioncontaining silicon abundantly in terms of composition and whose surfaceis a (001) crystal plane is formed on the surface of the substrate, acubic Group III nitride semiconductor junction layer is formed on thesurface of the silicon carbide layer, thereafter asuperlattice-structured layer constituted by cubic Group III nitridesemiconductor junction layers is formed on the Group III nitridesemiconductor junction layer, whereby a semiconductor device is formedthrough these steps. Therefore, it is possible to manufacture asemiconductor device capable of advantageously exhibiting optical orelectrical properties based on the crystal properties of the cubic GroupIII nitride semiconductor.

Particularly, according to the present invention, after the formation ofa silicon carbide layer which has a nonstoichiometric compositioncontaining silicon abundantly in terms of composition on the surface ofthe substrate, a Group III nitride semiconductor junction layer composedof aluminum nitride is formed by supplying a gaseous raw materialcontaining aluminum and a gaseous raw material containing nitrogen tothe surface of the silicon carbide layer. Accordingly, it is possible toreduce a lattice mismatch and, therefore, it is possible to manufacturea high-performance semiconductor device having a good-quality Group IIInitride semiconductor junction layer composed of AlN.

Particularly, according to the present invention, when after theformation of a silicon carbide layer which has a nonstoichiometriccomposition containing silicon abundantly in terms of composition on thesurface of the substrate, a Group III nitride semiconductor junctionlayer composed of AlN is formed on the surface of the silicon carbidelayer, an aluminum film is formed on the surface of the silicon carbidelayer by supplying a gaseous raw material containing aluminum andthereafter the aluminum film is nitrified by supplying a gaseousmaterial containing nitrogen to the film, whereby an aluminum nitridelayer is formed. Therefore, it is possible to form a Group III nitridesemiconductor layer from, for example, AlN whose crystal system isunified into a hexagonal system.

Particularly, according to the present invention, a hydrocarbon gas isblown onto the surface of the substrate composed of a silicon singlecrystal and hydrocarbon is caused to be adsorbed onto the surface of thesilicon single crystal substrate by radiating electrons onto the surfaceof the silicon single crystal substrate, whereby a cubic silicon carbidelayer whose lattice constant exceeds 0.436 nm and is not more than 0.460nm and which has a nonstoichiometric composition containing siliconabundantly in terms of composition is formed. Therefore, it is possibleto stably form a silicon carbide layer that has especially few crystaldefects and is excellent in crystallinity and hence it is possible tostably manufacture a high-performance semiconductor device.

Particularly, according to the present invention, after causing ahydrocarbon to be adsorbed onto the surface of the substrate composed ofa silicon single crystal by blowing a hydrocarbon gas while radiatingelectrons, the silicon single crystal substrate is heated to atemperature of not less than a temperature at which hydrocarbon iscaused to be adsorbed and a chemical reaction between the siliconforming the substrate and the hydrocarbon adsorbed onto the surface ofthe substrate is promoted, whereby a cubic silicon carbide layer isformed. Accordingly, it is possible to efficiently form a cubic siliconcarbide layer having few crystal defects and, therefore, it is possibleto stably manufacture a high-performance semiconductor device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of an LED described in Embodiment 1 ofthe present invention.

FIG. 2 is a schematic diagram showing a sectional structure taken alongthe broken line II-II of the LED shown in FIG. 1.

FIG. 3 is a schematic sectional view of an LED described in Embodiment 2of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Although it is possible to use silicon single crystals having crystalplanes of various kinds of plane directions as silicon singlesubstrates, a silicon crystal that can be most advantageously used as asubstrate in carrying out the present invention is a (001) or (111)single crystal whose surface is a (001) crystal plane or a (111) crystalplane. Also a silicon single crystal whose surface is inclined fromthese crystal planes can be adequately used as a substrate. A siliconsingle crystal substrate whose surface is inclined from the (001)crystal plane, for example, in the 2°<110> direction in terms of angle,is advantageous for obtaining a crystal layer having few antiphase grainboundaries (hereinafter abbreviated as “APDs”) (refer to MaterialsScience Series “Electronmicroscopy for Crystal—for MaterialsResearchers” written by Hiroyasu Saka, Nov. 25, 1997, issued byUchidarokakuho Pub. Co, LTd., first edition, pp. 64 and 65). In thepresent invention, a (001) silicon single crystal is used mainly forforming a semiconductor device that uses a cubic crystal layer. On theother hand, a (111) silicon single crystal is used mainly for forming asemiconductor device that uses a cubic crystal layer.

The conduction type of a silicon single crystal used as a substrate isnot considered. Silicon single crystals of both of the P type and the Ntype can be used as the substrate. Particularly, silicon single crystalsubstrates of low resistivity (specific resistance) having highconductivity can be advantageously used for fabricating semiconductorlight emitting devices such as LEDs and LDs. High-resistivity siliconsingle crystals can be used as substrates for semiconductor devices whenit is necessary to reduce the leak of current for operating devices(device operating current) to the substrate side. High-resistivitysilicon single crystals can be used, for example, as substrates forfabricating FETs (a high-resistivity P type or N type semiconductor maysometimes be referred to as the π type or the ν type, respectively(refer to “Optical Communication Engineering—Light Emitting Device andPhotodetector,” written by Hiroo Yonezu, May 20, 1995, issued by KougakuTosho Co. Ltd., 5^(th) edition, p. 317, foot note).

In the present invention, regardless of the plane direction of a crystalplane that forms the surface of a silicon single crystal used as asubstrate, a silicon carbide layer is provided on the surface of thesilicon single crystal. According to the Ramsdell notation system (referto “SiC Ceramic New Materials—Recent Developments” written and edited bythe 124^(th) Committee of High-Temperature Ceramic Materials of JapanSociety for the Promotion of Science, Feb. 28, 2001, issued byUchidarokakuho, first edition, pp. 13 to 16), a cubic crystal layerhaving a 3C-type crystal structure is most preferable. Whether thecrystal structure of silicon carbide layer is a 3C-type cubic siliconcarbide (3C—SiC) or, for example, a 4H-type or 6H-type hexagonal siliconcarbide (4H—SiC, 6H—SiC) can be judged by an analysis of an electrondiffraction pattern, for example.

It is preferred that a 3C—SiC layer be formed by using hydrocarboncaused to be adsorbed on the surface of a silicon single crystalsubstrate. Examples of hydrocarbon gases for causing hydrocarbon to beadsorbed include saturated aliphatic hydrocarbons, such as methane(molecular formula: CH₃), ethane (molecular formula: C₂H₆) and propane(molecular formula: C₃H₈), and unsaturated hydrocarbons, such asacetylene (molecular formula: C₂H₂). In addition, aromatic hydrocarbonsor alicyclic hydrocarbons are also available. However, acetylene, whichis decomposed and readily reacts with silicon can be most advantageouslyused. It is preferred that the temperature at which acetylene is causedto be adsorbed onto a (111) crystal plane of a (111) silicon singlecrystal be in the range from 400° C. to 600° C. The temperature suitablefor causing acetylene to be adsorbed onto a (001) crystal plane of a(001) silicon single crystal is higher than in the case of a (111)crystal plane and in the range from 450° C. to 650° C.

It is preferred that hydrocarbons such as acetylene be caused to beadsorbed onto a crystal plane forming the surface of a silicon singlecrystal substrate after the creation of a reconstruction structure. Forexample, it is preferred that hydrocarbon be caused to be adsorbed aftera 7×7-reconstruction structure is caused to appear on the surface formedfrom, for example, a (111) silicon single crystal substrate. A7×7-reconstruction structure can be formed by subjecting the (111)crystal plane forming the surface of, for example, a (111) singlecrystal to heat treatment in a high-vacuum environment of the order of10⁻⁶ pascals (pressure unit: Pa), for example, in a molecular beamepitaxial (hereinafter abbreviated as “MBE”) growth chamber at 750° C.to 850° C. The reconstruction structure on the surface of a siliconsingle crystal substrate can be identified by electron diffractionanalysis, such as reflection high energy electron diffraction(hereinafter abbreviated as “RHEED”).

After hydrocarbon is caused to be adsorbed onto a crystal surfaceforming the surface of a silicon single crystal substrate, the siliconsingle crystal substrate is heated, whereby the adsorbed hydrocarbon andthe silicon atom forming the substrate crystal are caused to react witheach other and a silicon carbide layer is formed. If on this occasionthe silicon single crystal substrate is heated at a relatively hightemperature, a silicon carbide layer that stoichiometrically containssilicon abundantly can be formed. The silicon single crystal substrateonto which hydrocarbon is caused to be adsorbed is formed by beingheated, for example, at 500° C. to 700° C. In proportion as thetemperature of this heating becomes higher, a silicon carbide layerwhich stoichiometrically contains silicon more abundantly can be formedin a short time. The degree to which a silicon carbide layerstoichiometrically contains silicon is reflected in the lattice constantof silicon carbide of a nonstoichiometric composition consisting of thesilicon carbide layer. In hydrocarbons of a nonstoichiometriccomposition, the more abundant the silicon content, the larger thelattice constant. The lattice constant of 3C—SiC of an equivalentcomposition is 0.43 nm (refer to “SiC Ceramic New Materials—RecentDevelopments” above, p. 340, Table 5.1.1), whereas a silicon carbidelayer of a nonstoichiometric composition related to the presentinvention is characterized by having lattice constants that exceed 0.436nm and are not more than 0.460 nm.

A cubic 3C-type silicon carbide layer having a lattice constant in theabove-described range has few lattice mismatches with a Group IIInitride semiconductor material forming a Group III nitride semiconductorjunction layer. Therefore, in forming a Group III nitride semiconductorjunction layer from a cubic zincblende crystal type GaN having a latticeconstant of, for example, 0.451 nm, a cubic 3C-type silicon carbidelayer having a lattice constant in the above-described range is usefulas a buffer layer excellent in lattice matching. Also, because thespacing of (110) crystal planes of a cubic 3C-type silicon carbide layerhaving a lattice constant in the above-described range substantiallycoincides with the a-axis of wurtzite crystal type hexagonal AlN and,this cubic 3C-type silicon carbide layer is advantageous also forforming a hexagonal Group III nitride semiconductor layer that forms aGroup III nitride semiconductor junction layer. Because in a siliconcarbide layer having a lattice constant outside of the above-describedrange, lattice mismatches with Group III nitride semiconductor materialsof both cubic and hexagonal crystal forms increase, the crystal qualityof a Group III nitride semiconductor junction layer formed on thissilicon carbide layer becomes worse remarkably and this is exceedinglydisadvantageous.

A silicon carbide layer of a nonstoichiometric composition that containssilicon abundantly compared to carbon can also be formed by causinghydrocarbon to be adsorbed onto the surface of a silicon single crystalsubstrate and thereafter heating the surface of the substrate bysupplying a gas containing silicon to the surface of the substrate. Forexample, a silicon carbide layer of a nonstoichiometric composition thatcontains silicon abundantly is formed by heating the surface of asilicon single crystal substrate onto which hydrocarbon is caused to beadsorbed while supplying silanes (molecular formula: SiH₄) thereto.Also, a silicon carbide layer of a nonstoichiometric composition thatcontains silicon abundantly can be formed by heating a silicon singlecrystal substrate onto which hydrocarbon is caused to be adsorbed whileradiating beams of silicon in an MBE growth chamber. The latticeconstant of a formed silicon carbide layer of a nonstoichiometriccomposition can be measured by analysis means, such as an electrondiffraction method.

In order to obtain a silicon carbide layer whose surface is a (001)crystal plane in forming a silicon carbide layer of a nonstoichiometriccomposition, a (001) silicon single crystal whose surface is a (001)crystal plane is used as a substrate. Also, in order to obtain a siliconcarbide layer whose surface is a (111) crystal plane in forming asilicon carbide layer of a nonstoichiometric composition, a (111)silicon single crystal whose surface is a (111) crystal plane is used asa substrate.

In forming a silicon carbide layer on the surface of a silicon singlecrystal substrate regardless of the plane direction of a crystal planeforming the surface, hydrocarbon is caused to be homogeneously adsorbedonto the surface of the substrate by blowing a hydrocarbon gas onto thesurface of the substrate while radiating electrons thereto. For example,thermoelectrons emitted from a metal that is electrically heated in avacuum are used as the electrons to be radiated. Electrons are radiatedat a uniform density onto the surface of a silicon single crystalsubstrate. Appropriate radiation densities range from 1×10¹² to 5×10¹³cm⁻². If the accelerated energy of electrons to be radiated is as low asless than approximately 100 electron volts (unit: eV), this does notallow hydrocarbon to be uniformly adsorbed onto the surface of a siliconsingle crystal substrate. On the other hand, if electrons whoseaccelerated energy exceeds 500 eV are radiated, the decomposition anddesorption of hydrocarbon are accelerated and this is disadvantageous.Therefore, it is preferred that the potential difference between anelectron source, for example, a tungsten (W) filament and a siliconsingle crystal substrate, which is an object to be irradiated, be notless than 100 volts (V) but not more than 500 V.

Also in heating a silicon single crystal substrate onto the surface ofwhich hydrocarbon is caused to adsorbed and thereby forming a 3C—SiClayer on the surface of the substrate, a 3C—SiC layer excellent incrystallinity, which has a low crystal defect density of twins, stackingfaults and the like, can be formed by radiating electrons. Appropriateradiation densities range from 1×10¹² to 5×10¹³ cm⁻². Also, 100 eV to500 eV are appropriate as the accelerated energy of electrons to beradiated.

A Group III nitride semiconductor layer composed ofAl_(x)Ga_(Y)In_(z)N_(1-α)M_(α) (0≦X, Y, Z≦1, X+Y+Z=1, the symbol Mdenotes a Group V element except nitrogen and 0≦α<1) is provided in asilicon carbide layer of a nonstoichiometric composition so as to bebonded thereto. The Al_(x)Ga_(Y)In_(z)N_(1-α)M_(α) that forms a GroupIII nitride semiconductor junction layer can be formed from, forexample, aluminum-gallium nitride (Al_(x)Ga_(Y)N: 0≦X, Y≦1, X+Y=1),gallium-indium nitride (Ga_(Y)In_(z)N: 0≦Y, Z≦1, Y+Z=1) and aluminumphosphate nitride (AlN_(1-α)P_(α)N: 0≦α≦1).

It is preferred that a Group III nitride semiconductor junction layer beformed from a Group III nitride semiconductor material having a latticeconstant or lattice plane spacing that approximates the lattice constant(=a) (that exceeds 0.436 and is not more than 0.460 nm) of a siliconcarbide layer of a nonstoichiometric composition. A Group III nitridesemiconductor junction layer can be advantageously formed from, forexample, cubic zincblende crystal type AlN (a=0.438 nm) and GaN (a=0.451nm). Also, a Group III nitride semiconductor junction layer can beformed from hexagonal wurtzite crystal type AlN, GaN and a mixed crystalof the two, which have an a-axis approximating the spacing (0.308 nm to0.325 nm) of (110) crystal planes of a cubic silicon carbide layerhaving a nonstoichiometric composition related to the present.

In forming a group III nitride semiconductor junction layer composed ofhexagonal AlN and the like, it is advisable to use a (111) siliconsingle crystal whose surface is a (111) crystal plane. Also, inobtaining a group III nitride semiconductor junction layer composed ofcubic AlN and the like, it is advantageous to use a (001) silicon singlecrystal whose surface is a (001) crystal plane.

Furthermore, in forming a group III nitride semiconductor junction layercomposed of AlN, it is possible to adopt a method that involvesdepositing an aluminum (Al) film on the surface of a silicon singlecrystal substrate and thereafter nitriding the Al film in an atmosphericfurnace of a nitrogen-containing gas. According to this forming method,it is possible to efficiently form an AlN layer with a unified crystalsystem by this forming method. For example, if an Al film is formed onthe surface of a (111) silicon single crystal substrate, which iscomposed of a (111) crystal plane, and thereafter the surface isnitrided in an nitrogen plasma atmosphere, then a hexagonal AlN layerwhose crystal system is unified into a hexagonal system can be formed.

A Group III nitride semiconductor junction layer formed with excellentmatching on a silicon carbide layer of a nonstoichiometric compositionpromotes the formation of a superlattice-structured layer provided as anupper layer of the Group III nitride semiconductor junction layer. AGroup III nitride semiconductor junction layer can be formed by usinggrowth methods, such as the metal organic chemical vapor deposition(hereinafter abbreviated as “MOCVD”) method, the halogen or hydridechemical vapor deposition (CVD) method, the MBE method and the chemicalbeam epitaxy method (hereinafter abbreviated as “CBE”) method.

A superlattice-structured layer constituted by Group III semiconductorsis formed on a Group III nitride semiconductor junction layer. Asuperlattice-structured layer is formed, for example, by alternatelystacking III Group nitride semiconductor layers having differentcompositions of constituent elements. Also, a superlattice-structuredlayer is formed by alternately stacking Group III nitride semiconductorlayers having different band gaps. When a Group III nitridesemiconductor junction layer is formed from AlN or GaN, it is preferredthat a superlattice-structured layer be constituted by Al_(x)Ga_(1-x)N(0≦X≦1) layers having different aluminum composition ratios (═X) interms of lattice matching. Also, it is preferred that asuperlattice-structured layer be constituted Ga_(Q)In_(1-Q)N (0≦Q≦1)layers having different gallium (Ga) composition ratios.

Particularly, a superlattice-structured layer that gives a Group IIInitride semiconductor layer excellent in surface flatness is obtained byproviding an Al_(x)Ga_(1-x)N layer having a minimum aluminum compositionratio among the Al_(x)Ga_(1-x)N layers of different aluminum compositionratios that constitute a superlattice-structured layer so as to bebonded to a Group III nitride semiconductor junction layer. Alsosimilarly, a superlattice-structured layer that gives a Group IIInitride semiconductor layer excellent in surface flatness is obtained byproviding a Ga_(Q)In_(1-Q) having a maximum gallium composition ratioamong the Ga_(Q)In_(1-Q)N (0≦Q≦1) layers of different galliumcomposition ratios that constitute a superlattice-structured layer.

Particularly, the propagation of strains in the interior of a crystallayer can be advantageously suppressed when a superlattice-structuredlayer is constituted by Al_(x)Ga_(1-x)N layers or Ga_(Q)In_(1-Q)N layershaving a film thickness of not less than 5 MLs but not more than MLs.Therefore, it is possible to form a superlattice-structured layer thatbrings about the formation of a group III nitride semiconductor layerexcellent in surface flatness. A thickness of 1 ML is a thickness of ½of a c-axis in a hexagonal Group III nitride semiconductor layer. Forexample, the thickness of 1 ML of a wurtzite crystal type GaN having ac-axis of 0.520 nm is 0.260 nm. This thickness corresponds to a latticeconstant in the case of a cubic Group III nitride semiconductor layer.

A superlattice-structured layer may also be of a quantum well structurethat gives a quantum level to an electron and a hole. When aquantum-well structure is foamed from Al_(x)Ga_(1-x)N (0≦X≦1) layers, anAl_(x)Ga_(1-x)N (0≦X≦1) layer having a higher aluminum composition ratio(═X) and a larger band gap is used as a barrier layer and anAl_(x)Ga_(1-x)N layer having a lower aluminum composition ratio (═X) anda smaller band gap is used as a well layer. Also, when a quantum wellstructure is formed from Ga_(Q)In_(1-Q)N (0≦Q≦1) layers, aGa_(Q)In_(1-Q)N layer having a higher gallium composition ratio (=Q) anda larger band gap is used as a barrier layer and having a lower galliumcomposition ratio (=Q) and a smaller band gap is used as a well layer.

As with the above-described Group III nitride semiconductor junctionlayer, Al_(x)Ga_(1-x)N layers or Ga_(Q)In_(1-Q)N layers that constitutea superlattice-structured layer can be formed by using growth methods,such as MOCVD method, halogen or hydride CVD method, MBE method and CBEmethod. A semiconductor device is readily obtained if asuperlattice-structured layer is continuously formed on the Group IIInitride semiconductor junction layer by using the same growth method asused in the formation of the above-described Group III nitridesemiconductor junction layer.

If in the growth of Al_(x)Ga_(1-x)N or Ga_(Q)In_(1-Q)N layers thatconstitute a superlattice-structure, these layers are grown by supplyingrepeatedly the raw materials of Group III elements and Group V elementthat constitute these layers, it is possible to obtain asuperlattice-structured layer excellent in surface flatness. Forexample, it is possible to obtain a superlattice-structured layerexcellent in surface flatness if Al_(x)Ga_(1-x)N or Ga_(Q)In_(1-Q)Nlayers are used which are formed by using a method that involves firstsupplying the raw materials of the Group III elements, thereafterstopping the supply of the raw materials of the Group III elements, andsupplying a nitrogen source in place of the raw materials of the GroupIII elements, that is, by alternately supplying the raw materials of theGroup III elements and the Group V element.

In convenient manufacturing semiconductor devices by using a simpleprocess, it is advisable to perform the cleaning of the surface of asilicon single crystal substrate, the adsorption of hydrocarbon onto thecleaned substrate surface, the formation of a silicon carbide layerusing the adsorbed hydrocarbon, the formation of a Group III nitridesemiconductor junction layer on the silicon carbide layer, and theformation of a superlattice-structured layer on the Group III nitridesemiconductor junction layer by using the same equipment consistently.If the MBE method is adopted, growth is caused to occur in a high-vacuumenvironment and, therefore, in causing hydrocarbon to be adsorbed andforming a silicon carbide layer on the basis of the adsorbedhydrocarbon, the radiation of electrons onto the surface of a siliconsingle crystal substrate can be readily performed. Also, the MBE methodhas the advantage that Al_(x)Ga_(1-x)N layers or Ga_(Q)In_(1-Q)N layersthat constitute a superlattice-structured layer can be readily formed byalternately supplying the raw materials of the constituent elements asdescribed above.

A grown layer excellent in surface flatness can be formed on asuperlattice-structured layer. Therefore, if such a grown layerexcellent in surface roughness is used as an active layer, it ispossible to form a semiconductor device having excellent optical orelectrical properties. A high-mobility FET can be formed if, forexample, a hexagonal Group III nitride semiconductor layer provided in asuperlattice-structured layer constituted by hexagonal Group III nitridesemiconductor layers on a hexagonal Group III nitride semiconductorjunction layer is utilized as an electron channel layer or an electronsupply layer. Particularly, it is possible to manufacture ahigh-mobility FET having an electron channel layer that efficientlyaccumulates two-dimensional electrons due to the occurrence of thepiezoelectric effect caused by a hexagonal Group III nitridesemiconductor.

Also, it is possible to form high-luminance light emitting devices, suchas LEDs, if for example a cubic Group III nitride semiconductor layerprovided in a superlattice-structured layer constituted by cubic GroupIII nitride semiconductor layers on a cubic Group III nitridesemiconductor junction layer is utilized as a lower cladding layer or alight limiting layer. Particularly, an LD with a unified oscillationwavelength can be formed by utilizing the properties of a cubic GroupIII nitride semiconductor with a degenerated valence band.

Next, embodiments of the present invention will be described. Thepresent invention, however, is not limited by these embodiments.

Embodiment 1

In Embodiment 1, the present invention will be described in detail bytaking, as an example, a case where a light emitting diode (LED) isfabricated from an epitaxially stacked structure including a siliconcarbide layer of a nonstoichiometric composition provided on a (111)silicon single crystal substrate whose surface is a (111) crystal plane,a hexagonal Group III nitride semiconductor junction layer, asuperlattice-structured layer constituted by hexagonal Group III nitridesemiconductor layers.

The plane structure of a semiconductor LED 10 fabricated in Embodiment 1is schematically shown in FIG. 1. The sectional structure of the LED 10of FIG. 10 taken along the broken line II-II is schematically shown inFIG. 2.

In the fabrication of the LED 10, a P type silicon single crystal havinga (111) crystal plane as the surface, to which boron (element symbol: B)is added, was used as a substrate 101. After the substrate 101 wastransported into a growth chamber for MBE growth, the substrate 101 washeated to 850° C. in a high vacuum of approximately 5×10⁻⁷ pascals (Pa).Heating at the same temperature was continued while an RHEED pattern wasbeing monitored until the (111) crystal plane forming the surface of thesubstrate 101 obtained a 7×7-reconstruction structure.

After the appearance of the 7×7-rearranged structure was ascertained,the temperature was lowered to 450° C., with the substrate 101 kept inthe MBE growth chamber. Next, an acetylene gas was blown onto thesurface of the substrate 101 and acetylene was caused to be adsorbedonto the surface. The acetylene gas was continuously blown until anelectron diffraction spot originated from the 7×7-reconstructionstructure of the surface of the substrate 101 almost disappeared on theRHEED pattern.

After that, the blowing of the acetylene gas onto the surface of thesubstrate 101 was stopped and the substrate 101 was heated to 600° C.Until a streak due to the cubic 3C-type silicon carbide appeared on theRHEED pattern, the substrate 101 was held at the same temperature and asilicon carbide layer 102 was formed on the surface of the siliconsingle crystal substrate 101. At 600° C., the lattice constant of theformed silicon carbide was calculated to be 0.450 nm on the basis of thelattice constant of the silicon single crystal found from the RHEEDpattern of the (111) silicon single crystal. The layer thickness of thesilicon carbide layer 102 was approximately 2 nm and the surface of thelayer 102 was a (111) crystal plane.

On the silicon carbide layer 102 of a nonstoichiometric composition, awurtzite crystal type hexagonal aluminum nitride (AlN) layer 103 wasformed by the MBE method using a nitrogen plasma as a nitrogen source,with the temperature of the substrate 101 raised to 700° C. The nitrogenplasma was generated by using an electron cyclotron resonance (ECR) typeapparatus that applies a high-frequency wave with a frequency of 13.56MHz and a magnetic field to a high-purity nitrogen gas. With the MBEgrowth chamber kept at a high vacuum of approximately 1×10⁻⁶ Pa, theatomic nitrogen (nitrogen radical) within the nitrogen plasma wasextracted by using an electrical repulsive force and sputtered onto thesurface of the silicon carbide layer 102. The layer thickness of the AlNlayer 103 formed as a Group III nitride semiconductor junction layermentioned in the present invention was approximately 15 nm and thesurface of the AlN layer 103 was a (0001) crystal plane.

On the hexagonal AlN layer 103, a first N type hexagonal gallium nitride(GaN) 104 a was formed at 720° C. by the MBE method. The layer thicknessof the first N type GaN layer 104 a, which is a constituent layer of asuperlattice-structured layer 104, was set at 10 ML (approximately 2.6nm). A first N type aluminum gallium nitride mixed crystal(Al_(0.10)Ga_(0.90)N) 104 b with an aluminum (Al) composition ratio of0.10, which is another constituent layer constituting thesuperlattice-structured layer 104, was provided so as to be bonded tothe first N type GaN layer 104 a. Next, a second N type GaN layer 104 awas provided so as to be bonded to the first N type Al_(0.10)Ga_(0.9)Nmixed crystal layer 104 b. A second N type Al_(0.10)Ga_(0.90)N mixedcrystal layer 104 b was provided so as to be bonded to the second N typeGaN layer 104 a. Furthermore, on the second N type Al_(0.10)Ga_(0.90)Nmixed crystal layer 104 b, a third N type GaN layer 104 a and a third Ntype Al_(0.10)Ga_(0.90)N mixed crystal layer 104 b were provided,whereby the formation of the superlattice-structured layer 104 wascompleted. The layer thickness of all of the first to third N typeAl_(0.10)Ga_(0.90)N mixed crystal layers 104 b was set at 10 ML.

On the superlattice-structured layer 104, a lower cladding layer 105composed of N type GaN with a layer thickness of approximately 2200 nmwas provided by the MBE method while silicon (Si) was being doped.Because the N type GaN layer 105 was provided via the above-describedsuperlattice-structured layer 104, the N type GaN layer 105 hadexcellent flatness with roughness of approximately 1.0 nm in terms ofthe RMS-value.

On the lower cladding layer 105, a light emitting layer 106 of amulti-quantum well structure obtained by alternately stacking an N typeGaN as a buffer layer and an N type gallium-indium nitride mixed crystal(Ga_(0.85)In_(0.15)N) as a well on five cycles was formed. On the lightemitting layer 106, an upper cladding layer 107 composed of P typeAl_(0.10)Ga_(0.90)N (layer thickness: approximately 90 nm) was formed.As a result, a light emitting part of a PN junction type double-hetero(DH) junction structure was constituted by the N type cladding layer105, the N type light emitting layer 106 and the P type upper claddinglayer 107. On the P type upper cladding layer 107 that forms the lightemitting part, a contact layer 108 composed of P type GaN (layerthickness: approximately 100 nm) was further provided, whereby a stackedstructure 11 for the LED 10 was formed.

On the surface of the P type contact layer 108 forming the uppermostsurface of the stacked structure 11, a P type ohmic electrode 109composed of gold (element symbol: Au) and a nickel (element symbol: Ni)oxide was formed. An N type ohmic electrode 110 was formed after theremoval of the light emitting layer 106, the upper cladding layer 107and the contact layer 108, which were present in the region where theelectrode 110 was to be provided, by use of general dry etching means.Because the N type ohmic electrode 110 was formed via thesuperlattice-structured layer 104, the N type ohmic electrode 110 wasprovided on the lower cladding layer 105, which obtained excellentflatness. That is, in the LED 10, the P type ohmic electrode 109 and theN type ohmic electrode were provided on the same front surface side withrespect to the silicon single crystal substrate 101.

An device operating current was flown across the P type and N type ohmicelectrodes 109, 110 of the LED chip fabricated as described above, andluminescent and electrical properties were investigated. When a currentwas flown through the LED 10 in the forward direction, blue light havinga dominant wavelength of 460 nm was emitted. The luminescence intensityobtained when the forward-direction current was 20 mA, was as high asapproximately 2.2 mW. The forward-direction voltage (Vf) obtained when acurrent of 20 mA was caused to flow in the forward direction, becameapproximately 3.4 V. Because the silicon carbide layer 102 of anonstoichiometric composition was provided as the buffer layer, it waspossible to provide the superlattice-structured layer 104 and the lightemitting part having the DH structure, which were formed from Group IIIsemiconductor layers excellent in crystallinity, on the silicon carbidelayer 102. For this reason, the reverse-direction voltage obtained whena reverse-direction current was set to 10 μA, became as high as 15 V.Also, because particularly the superlattice-structured layer 104 and thelight emitting part were constituted by Group III semiconductor layersexcellent in crystallinity, it was possible to obtain an LED excellentin reverse-direction breakdown voltage properties, which issubstantially free from local breakdowns.

Embodiment 2

In Embodiment 2, the present invention will be described in detail bytaking, as an example, a case where a light emitting diode (LED) isfabricated from an epitaxially stacked structure including a siliconcarbide layer of a nonstoichiometric composition provided on a (001)silicon single crystal substrate whose surface is a (001) crystal plane,a cubic Group III nitride semiconductor junction layer, asuperlattice-structured layer constituted by cubic Group III nitridesemiconductor layers.

The planar structure of a semiconductor LED 10 fabricated in Embodiment2 is schematically shown in FIG. 2.

In the fabrication of the LED 20, an N type silicon single crystalhaving a (001) crystal plane as the surface, to which phosphorus(element symbol: P) is added, was used as a substrate 201. After thesubstrate 201 was transported into a growth chamber for MBE growth, thesubstrate 201 was heated to 800° C. in a high vacuum of approximately5×10⁻⁷ pascals (Pa). Heating at the same temperature was continued whilean RHEED pattern was being monitored until the (001) crystal planeforming the surface of the substrate 201 obtained a 2×1-reconstructedstructure.

After the appearance of the 2×2-reconstructed structure was ascertained,the temperature was lowered to 420° C., with the substrate 201 kept inthe MBE growth chamber. Next, an acetylene gas was blown onto thesurface of the substrate 201 while electrons were being radiated, andacetylene was caused to be adsorbed onto the surface. The electrons weregenerated by electric heating of tungsten (element symbol: W) arrangedin the growth chamber maintained in a vacuum. The electrons wereradiated at an accelerated voltage of 300 V and with an area density ofapproximately 5×10¹² cm⁻². The acetylene gas and electrons werecontinuously supplied until an electron diffraction spot caused by the2×1-reconstruction structure of the surface of the substrate 201 almostdisappeared on the RHEED pattern.

After that, the silicon single crystal substrate 201 was heated to 550°C. When the temperature of the substrate 201 became stable at 550° C.,electrons started to be radiated again onto the substrate 201. Until astreak due to the cubic 3C-type silicon carbide appeared on the RHEEDpattern, the radiation of electrons onto the surface of the substrate201 was continued, whereby a 3C-type cubic silicon carbide layer 202 wasformed on the surface of the silicon single crystal substrate 201. At600° C., the lattice constant of the formed silicon carbide wascalculated to be 0.440 nm on the basis of the lattice constant of thesilicon single crystal found from the RHEED pattern of the (001) siliconsingle crystal. No extra diffraction caused by twins and stacking faultswas observed in the RHEED pattern of the silicon carbide layer 202. Thelayer thickness of the silicon carbide layer 202 was approximately 2 nmand the surface of the layer 202 was a (001) crystal plane.

On the silicon carbide layer 202 of a nonstoichiometric composition, acubic zinc blende crystal type aluminum nitride (AlN) layer 203 wasformed by the MBE method using a nitrogen plasma as a nitrogen source,with the temperature of the substrate 201 raised to 700° C. The nitrogenplasma was generated by using an electron cyclotron resonance (ECR) typeapparatus that applies a high-frequency wave with a frequency of 13.56MHz and a magnetic field to a high-purity nitrogen gas. With the MBEgrowth chamber kept in a high vacuum of approximately 1×10⁻⁶ Pa, theatomic nitrogen (nitrogen radical) within the nitrogen plasma wasextracted by using an electrical repulsive force and sputtered onto thesurface of the silicon carbide layer 202. The layer thickness of the AlNlayer 203 formed as a Group III nitride semiconductor junction layermentioned in the present invention was set at approximately 8 nm and thesurface of the AlN layer 203 was a single crystal layer whose surface isa (001) crystal plane.

On the (001) crystal plane of the surface of the cubic AlN layer 203, afirst N type cubic gallium nitride (GaN) 204 a was formed at 700° C. bythe MBE method. The layer thickness of the first N type GaN layer 204 a,which is a constituent layer of a superlattice-structured layer 204, wasset at 15 ML (approximately 3.9 nm). A first N type gallium indiumnitride mixed crystal (Ga_(0.95)In_(0.05)N) 204 b with a gallium (Ga)composition ratio of 0.95, which is another constituent layerconstituting the superlattice-structured layer 204, was provided so asto be bonded to the first N type GaN layer 204 a. Next, a second N typeGaN layer 204 a was provided so as to be bonded to the first N typeGa_(0.95)In_(0.05)N mixed crystal layer 204 b. A secondGa_(0.95)In_(0.05)N mixed crystal layer 204 b was provided so as to bebonded to the second N type GaN layer 204 a. Furthermore, on the secondGa_(0.95)In_(0.05)N mixed crystal layer 204 b, a third N type GaN layer204 a and a third N type Ga_(0.95)In_(0.05)N mixed crystal layer 204 bwere provided, whereby the formation of the superlattice-structuredlayer 204 was completed. The layer thickness of all of the first tothird N type Ga_(0.95)In_(0.05)N mixed crystal layers 204 b was set at10 ML.

On the second Ga_(0.95)In_(0.05)N mixed crystal layer 204 b whosesurface is a (001) crystal plane, which forms the uppermost surface ofthe superlattice-structured layer 204, a lower cladding layer 205 formedfrom N type cubic GaN with a layer thickness of approximately 1800 nmwas provided by the MBE method while silicon was being doped. Becausethe N type GaN layer 205 was provided via the above-describedsuperlattice-structured layer 204, the N type GaN layer 205 had goodflatness with surface roughness of approximately 1.2 nm in terms of RMS.

On the lower cladding layer 205, a light emitting layer 206 of amulti-quantum well structure constituted by five pairs of cubic N typeGaN barrier layers and cubic N type gallium indium nitride mixedcrystals (Ga_(0.85)In_(0.15)N) well layers were formed at 700° C. by theMBE method. On the light emitting layer 206, an upper cladding layer 207composed of cubic P type Al_(0.10)Ga_(0.90)N was formed. As a result, alight emitting part of a PN junction type double-hetero (DH) junctionstructure was constituted by the N type cladding layer 205, the N typelight emitting layer 206 and the P type upper cladding layer 207. On theP type upper cladding layer 207 that forms the light emitting part, acontact layer 208 composed of cubic P type GaN with a layer thickness ofapproximately 90 nm was further provided by the MBE method, whereby astacked structure 21 for the LED 20 was formed.

In the middle of the surface of the P type contact layer 208 forming theuppermost surface of the stacked structure 21, a P type ohmic electrode209 composed of gold (Au) and an nickel (Ni) oxide was formed. An N typeohmic electrode 210 was formed by providing a gold vacuum evaporatedfilm on the whole area of the rear surface of the N type silicon singlecrystal substrate 201.

A device operating current was caused to flow across the P type and Ntype ohmic electrodes 209, 210 of the LED chip 20 fabricated asdescribed above, and luminescent and electrical properties wereinvestigated. When a current was flown through the LED 20 in the forwarddirection, blue light having a dominant wavelength of 465 nm wasemitted. The luminescence intensity obtained when the forward-directioncurrent was 20 mA, was as high as approximately 2.0 mW. Theforward-direction voltage (Vf) obtained when a current of 20 mA wasflown in the forward direction became approximately 3.3 V. Because thesilicon carbide layer 202 of a nonstoichiometric composition wasprovided as the buffer layer, it was possible to provide thesuperlattice-structured layer 204 and the light emitting part having theDH structure, which were composed of Group III semiconductor layersexcellent in crystallinity, on the silicon carbide layer 202. For thisreason, the reverse-direction voltage obtained when a reverse-directioncurrent was 10 μA, became as high as 15 V. Also, because particularlythe superlattice-structured layer 204 and the light emitting part wereconstituted by Group III nitride semiconductor layers excellent incrystallinity, it was possible to obtain an LED excellent inreverse-direction breakdown voltage properties, which is substantiallyfree from local breakdowns.

Embodiment 3

The present invention in this embodiment will be concretely described bytaking, as an example, a case where an LED having a Group III nitridesemiconductor junction layer composed of aluminum nitride formed bynitriding a metal aluminum film is fabricated.

As described in Embodiment 1 above, a cubic 3C-type silicon carbidelayer was formed on a (111) silicon single crystal substrate whosesurface is a (111) crystal plane. Next, within an MBE growth chamber,aluminum (Al) beams were radiated onto the surface formed from a (111)crystal plane of the silicon carbide layer having a lattice constant of0.450 nm, whereby an Al film was formed. The film thickness of the Alfilm was set at approximately 3 nm.

Next, by use of an ECR (electron cyclotron resonance) typeradio-frequency (RF) plasma generator provided in the MBE growthchamber, a nitrogen plasma was generated within the chamber. After that,nitrogen radicals in the nitrogen plasma were selectively extracted andradiated onto the above-described Al film, which was nitrided thereby.It was ascertained from an RHEED pattern that the AlN film formed bynitriding is composed of a hexagonal crystal.

With the hexagonal AlN layer formed by nitriding the Al film serving asa Group III nitride semiconductor junction layer, asuperlattice-structured layer, an N type lower cladding layer, an N typelight emitting layer, a P type upper cladding layer and a P type contactlayer of exactly the same configuration as described in Embodiment 1above were stacked in order, whereby a stacked structure for LED wasformed. By using the AlN layer formed by nitriding as the Group IIInitride semiconductor junction layer, all of the Group III nitridesemiconductor layers constituting the above-describedsuperlattice-structured layer and the like provided on the AlN layerwere unified into a hexagonal system. According to an electrondiffraction analysis and a general cross-sectional TEM (transmissionelectron microscope) observation, the surfaces of these layers were(0001) crystal planes and the presence of cubic crystalline granules wasscarcely observed.

On the above-described stacked structure having the hexagonal AlN layerformed by nitriding as the group III nitride semiconductor junctionlayer, P type and N type ohmic electrodes were provided as described inEmbodiment 1 above and an LED was formed thereby.

The luminescence wavelength observed when a forward-direction currentwas flown through the LED, was approximately 460 nm, almost the samevalue as with the LED described in Embodiment 1 above. Furthermore,because the AlN layer that was formed by the nitriding of the Al filmand whose crystal system was unified into a hexagonal system, was usedas the Group III nitride semiconductor junction layer, the lightemitting layer was formed from hexagonal Group III nitride semiconductorcrystals substantially free from the mixing of cubic crystallinegranules. Therefore, the luminescence wavelength between LED chips wasuniform.

In the semiconductor device of the present invention, a silicon singlecrystal is used as a substrate, and a buffer layer is formed from cubicsilicon carbide which is provided on the substrate, whose latticeconstant exceeds 0.436 nm and is not more than 0.460 nm, and which has anonstoichiometric composition containing silicon abundantly in terms ofcomposition, a Group III nitride semiconductor junction layer composedof Al_(x)Ga_(Y)In_(z)N_(1-α)M_(α) is provided on the buffer layer, and asuperlattice-structure constituted by Group III nitride semiconductorsis provided on the Group III nitride semiconductor junction layer. Thesemiconductor device is obtained by using this stacked structure.Therefore, it is possible to form a Group III nitride semiconductorlayer excellent in crystallinity and in surface flatness as well.Therefore, a high-performance semiconductor device is obtained.

1. A semiconductor device comprising a silicon single crystal substrate,a silicon carbide layer provided on a surface of the substrate, a GroupIII nitride semiconductor junction layer provided in contact with thesilicon carbide layer, and a superlattice-structured layer constitutedby Group III nitride semiconductors on the Group III nitridesemiconductor junction layer, wherein the silicon carbide layer is alayer of a cubic system whose lattice constant exceeds 0.436 nm and isnot more than 0.460 nm and which has a nonstoichiometric compositioncontaining silicon abundantly in terms of composition, and the Group IIInitride semiconductor junction layer has a composition ofAl_(x)Ga_(Y)In_(z)N_(1-α)M_(α) (0≦X, Y, Z≦1, X+Y+Z=1, 0≦α<1, M is aGroup V element except nitrogen).
 2. The semiconductor device accordingto claim 1, wherein the superlattice-structured layer constituted byGroup III nitride semiconductors is a layer formed by alternatelystacking aluminum gallium nitride (Al_(x)Ga_(1-x)N: 0≦X≦1) layers havingdifferent aluminum (Al) composition ratios.
 3. The semiconductor deviceaccording to claim 2, wherein a layer having a low Al composition ratioamong the aluminum-gallium nitride layers having different aluminumcomposition ratios is in contact with the Group III nitridesemiconductor junction layer.
 4. The semiconductor device according toclaim 1, wherein the superlattice-structured layer constituted by GroupIII nitride semiconductors is a layer foamed by alternately stackinggallium indium nitride (Ga_(Q)In_(1-Q)N: 0≦Q≦1) layers having differentgallium (Ga) composition ratios.
 5. The semiconductor device accordingto claim 4, wherein a layer having a high gallium (Ga) composition ratioamong the gallium indium nitride layers having different gallium (Ga)composition ratios is in contact with the Group III nitridesemiconductor junction layer.
 6. The semiconductor device according toclaim 1, wherein the superlattice-structured layer constituted by GroupIII nitride semiconductors has a film thickness in the range from 5monolayers (MLs) to 30 MLs.
 7. The semiconductor device according toclaim 1, wherein the silicon single crystal substrate is a substratewhose surface is a (111) crystal plane, and the Group III nitridesemiconductor junction layer is a hexagonal wurtzite crystal typealuminum nitride (AlN) layer.
 8. The semiconductor device according toclaim 1, wherein the silicon single crystal substrate is a substratewhose surface is a (001) crystal plane, and the Group III nitridesemiconductor junction layer is a cubic zinc blende crystal typealuminum nitride (AlN) layer.
 9. (canceled)
 10. (canceled) 11.(canceled)
 12. (canceled)
 13. (canceled)
 14. (canceled)
 15. (canceled)16. (canceled)